1. Field of the Invention
This invention relates to a four-stroke reciprocating piston internal combustion engine in which fuel and exhaust vapors are purged from the engine manifolds and each cylinder when the engine is turned off or in a shutdown condition in order to minimize emissions on subsequent engine startup.
2. Description of the Related Art
Conventional internal combustion engine startup is notoriously dirty in terms of emissions. Remnant fuel and exhaust vapors from previous engine operation are typically trapped in the intake manifold and cylinders when the conventional internal combustion engine is turned off. These remaining vapors, which are subsequently forced out of the engine and through a cold, ineffective catalytic converter at engine startup, are a significant contribution to the overall emissions detected during standardized emissions tests.
What is needed, therefore, is a clean internal combustion engine shutdown method wherein fuel and exhaust vapors that would normally be trapped in the intake manifold and cylinders when the engine is turned off or in a shutdown condition are instead expelled through the warm catalytic converter when the engine is shut down, thereby producing a noticeable improvement in engine emissions during engine startup.
The foregoing needs are met by a four-stroke reciprocating internal combustion engine including a combustion chamber defined by a cylinder, a reciprocating piston contained within the cylinder, and a cylinder head. The engine includes an exhaust port in fluid communication with the combustion chamber and an exhaust manifold, which is in fluid communication with an emissions control device. The exhaust port includes an exhaust valve for controlling the release of gases from the combustion chamber. The engine also includes an intake port in fluid communication with the combustion chamber. The intake port is in fluid communication with a fuel injector for directing fuel into air in the intake port to form an air-fuel mixture. The intake port includes an intake valve for controlling the induction of the air-fuel mixture into the combustion chamber. The engine cylinder includes a spark device for igniting the air-fuel mixture introduced into the combustion chamber through the intake port. In an alternative version of the engine, the fuel injector is in fluid communication with the combustion chamber and directs fuel into air inducted into the combustion chamber through the intake port. The engine further includes at least one sensor for sensing at least one engine operating condition.
Operation of the engine is controlled by an engine controller which is responsive to each sensor. The controller provides fuel injector control signals to the fuel injector for operating the fuel injector, spark device control signals to the spark device for operating the spark device, and valve control signals to a variable valve timing system for operating the exhaust valve and the intake valve. The controller executes a stored program including an engine shutdown sequence in which the controller: (a) senses when the engine is in a shutdown condition, (b) thereafter stops providing a fuel control signal to the fuel injector thereby ceasing fuel injection from the fuel injector, (c) thereafter provides a signal to operate the spark device to ignite the air-fuel mixture in the combustion chamber, (d) thereafter provides a signal to open the exhaust valve, (e) thereafter provides a signal to close the exhaust valve after the reciprocating piston has been in upward motion for a time period, (f) thereafter provides a signal to open the intake valve when the reciprocating piston is in downward motion, (g) thereafter provides a signal to close the intake valve after the reciprocating piston has been in downward motion for a time period, and (h) thereafter provides a signal to open the exhaust valve when the reciprocating piston is in upward motion.
The engine shutdown sequence that is initiated by the engine controller when the engine is in a shutdown condition serves to expel fuel and exhaust vapors, which would normally be trapped in the intake manifold and cylinders of a conventional engine, through the warm catalytic converter. During the engine shutdown sequence, the opening and closing of the intake valve and the exhaust valve are timed to induct air and any other vapors into the combustion chamber from the intake port and to thereafter expel the contents of the combustion chamber out through the exhaust port, the exhaust manifold, and the emissions control device. In one version of the invention, the engine shutdown sequence is programmed such that the intake valve opens after Top Dead Center (TDC) and closes prior to Bottom Dead Center (BDC) of the piston and the exhaust valve opens after BDC and closes prior to TDC of the piston. The timing of the opening and closing of the intake valve during downward motion of the piston and the timing of the opening and closing of the exhaust valve during upward motion of the piston can be varied infinitely because of the use of a variable valve timing system. In an example embodiment of the invention, the engine shutdown sequence is programmed such that the intake valve opens just after TDC (e.g., within 5 degrees of TDC) and closes just prior to BDC (e.g., within 5 degrees of BDC) of the piston and the exhaust valve opens just after BDC (e.g., within 5 degrees of BDC) and closes just prior to TDC (e.g., within 5 degrees of TDC) of the piston. This allows for complete cycling of intake air through the cylinder minimizing pumping losses. In the engine shutdown sequence, the inertia stored in the engine is used to breath the cylinders and manifolds during an engine shutdown condition.
It is therefore an advantage of the invention to provide a four-stroke reciprocating piston internal combustion engine in which fuel and exhaust vapors are purged from the engine manifolds and each cylinder when the engine is shut down in order to minimize emissions on subsequent engine startup.
It is another advantage of the invention to provide a clean internal combustion engine shutdown method wherein fuel and exhaust vapors that would normally be trapped in the intake manifold and cylinders when the engine is turned off or in a shutdown condition are instead expelled through the warm catalytic converter when the engine is shut down, thereby producing a noticeable improvement in engine emissions during engine startup.